Gaseous fuel powered engines are common in many applications. For example, the engine of a locomotive can be powered by natural gas (or another gaseous fuel) alone, or by a mixture of natural gas and diesel fuel. Natural gas may be more abundant and, therefore, less expensive than diesel fuel. In addition, natural gas may burn cleaner in some applications.
Natural gas, when used in a mobile application, may be stored in a liquid state onboard the associated machine. This may require the natural gas to be stored at cold temperatures, typically about −100 to −162° C. The liquefied natural gas (LNG) may then be drawn from the tank by gravity and/or by a boost pump and directed to a high-pressure pump. The high-pressure pump further increases a pressure of the fuel and directs the fuel to the machine's engine. In some applications, the liquid fuel is gasified prior to injection into the engine and/or mixed with diesel fuel (or another fuel) before combustion.
One problem associated with conventional high-pressure pumps involves lubricating the moving parts of the pump. Generally tight tolerances between moving parts, such as between plungers that reciprocate within barrels of pumping mechanisms, may create friction between the moving parts, thereby requiring more energy to drive the pump. Further, the friction may cause scuffing, wearing, and/or sticking of the plungers, barrels, or seals between the plungers and barrels, which can reduce the lifespan of the pump. Whereas diesel fuel may be more naturally lubricious and may lubricate plungers, barrels, and seals during operation of the pump, gaseous fuels generally have lower lubricity and may not provide sufficient lubrication.
One attempt to reduce friction within a fuel pump is disclosed in U.S. Pat. No. 7,134,851 (the '851 patent) that issued to Chenoweth on Nov. 14, 2006. In particular, the '851 patent discloses a reciprocating pump having a pump body and a plunger housing disposed in the pump body. The plunger housing defines a bore, and a plunger slides within the bore to draw fuel through an inlet of the pump and force the fuel through an outlet. A relatively small clearance is maintained between the plunger and the bore of the plunger housing to prevent leakage past the plunger. The plunger and/or plunger housing are formed of a ceramic material to reduce wear of the plunger and the cylinder.
While the pump of the '851 patent may reduce some fuel leakage and wearing of the plunger and/or plunger housing, it may not be suitable for primping low-temperature cryogenic fluids, such as LNG. Particularly, ceramic plungers and plunger housings may not be sufficiently lubricious at cryogenic temperatures to prevent wearing or sticking. Further, a difference in thermal expansion between ceramic plungers and plunger housings over a range of working temperatures may cause fuel leakage or wearing, thereby reducing the overall efficiency of the pump.
The disclosed pump is directed to overcoming one or more of the problems set forth above and/or other problems of the prior art.